Recording sheets, to be used in the image forming apparatuses, tend to absorb environmental moisture, due to the environment and the storage conditions. In case that a recording sheet is picked up to be conveyed from a bundle of sheets, accommodated in a sheet supplying section of the image forming apparatus, and is used for the image formation, if said bundle of recording sheets has absorbed moisture under a high humidity environment, due to moisture existing between the recording sheets, the recording sheets tend to adhere to each other. When said recording sheet is conveyed through the image forming apparatus, said recording sheet adheres to the next recording sheet, so that plural recording sheets are simultaneously conveyed, which conveyance is so called “double sheet conveyance”, further, a sheet conveying timing delay in the image forming apparatus tends to occur, which become major problems.
In recent years, high glossy images are requested for printing catalogues or posters. Coated printing sheets are used for this purpose. The coated printing sheet, having a resin coat on the surface, has higher flatness than a normal sheet. Accordingly, the coated printing sheets have higher adherence to each other than normal sheets. When said coated printing sheet is to be supplied from the sheet supplying section of the image forming apparatus, the above described double sheet conveyance and the sheet conveying timing delay tend to occur. In particular, under high humidity conditions, since the recording sheets, including the coated printing sheets, absorb moisture, and strongly adhere to each other, whereby the above described adverse problems tend to occur.
To overcome these problems, concerning image forming apparatuses, described in Japanese Unexamined Patent Application Publications 7-157120 and 2006-264918 (hereinafter referred to as JPA 120 and JPA 918), the sheet supplying section is formed to be a sealed structure, and a dehumidification heater is arranged in the sheet supplying section, so that widely varying types of recording sheets are dehumidified.
In the image forming apparatus described in above JPA 120, the inside of the apparatus is sealed by a cover member and a lower frame, and a partitioning plate is arranged between an upper mechanical section of the apparatus and the sheet supplying section, accommodating plural sheet supplying trays, so that ambient air cannot enter the inside of the sheet supplying device. Further, a heat generating body, installed in the lower frame, allows air to make convection in the inside of the sheet supplying device, so that the recording sheets, accommodated in each tray, are dehumidified.
In the image forming apparatus described in above JPA 918, a conveying path, for conveying the recording sheet to the image farming section, is closed or opened by a shutter, whereby a sheet supplying section, accommodating a dehumidification heater, is tightly sealed, and the recording sheets, stacked on the plural sheet supplying trays, are effectively dehumidified.
However, in order to make smooth sheets, such as coated printing sheets, to decrease adherence to each other, and to stably supply the sheets, the inside of the sheet supplying section must be heated to about 50° C. In the image forming apparatuses, described in JPA 120 and JPA 918, the temperature of the partitioning plate, above the sheet supplying section, reaches more than 50° C. The image forming section receives the heat, coming from the partitioning plate, and the temperature of the image forming section increases, so that adverse problems occur, relating to a photosensitive body and image forming processes around the photosensitive body. In particular, if low temperature melting toner is used in the image funning section, said problems occur notably.
In order to overcome these problems relating to the heat, there are ideas to increase the heat insulating properties of the partitioning plate, or to cool the image forming section. To realize those ideas, the apparatus becomes complicated.